Wavelength division multiplexing (WDM) is useful for increasing communication bandwidth by sending multiple data channels down a single fiber. For example, a 100 gigabit per second (Gbps) link can be constructed by using four channels operating at 25 Gbps per channel, with each channel operating at a different wavelength. A multiplexer is used to join the signals together before transmitting them down the waveguide, and a demultiplexer is subsequently used to separate the signals.